The overall objective of these studies is twofold: (a) to elucidate the biological significance of the presence in higher organisms (including human) of both the hormone-like polypeptide, epidermal growth factor (EGF), and receptors for this peptide. At the molecular level we hope to understand the biochemical steps leading from the binding of EGF by receptors on the cell membrane to the induction of DNA synthesis, and (b) to elucidate the biological significance of the presence of a putative membrane- spanning 120,000 MW precursor to EGF. EGF is a very potent mitogen for a variety of cells both in vivo and in cell culture. The amino acid sequence and many of the chemical and physical properties of this molecule have been determined. The binding and internalization of EGF have been described in detail. The interaction of EGF with responsive cells is one of the few instances in biology in which a direct effect of a hormone may be demonstrated in a cell free system. The plasma membrane receptor for EGF is a tyrosine specific protein kinase whose activity is enhanced by binding EGF. The EGF receptor/kinase has been isolated from A-431 cells and mouse liver; the receptor and kinase are parts of the same 170,000 MW glycoprotein. Our specific aims include: (1) Isolate, characterize, and prepare antibodies to preproEGF from kidney and from NIH 3T3 cells transfected with the cDNA of human preproEGF. Determine whether preproEGF is a membrane protein, whether it is glycosylated, and whether it has other functions in addition to serving as a precursor to EGF. (2) Identify, isolate and characterize cellular components phosphorylated by the EGF-receptor/tyrosine kinase. (3) Examine the mechanisms by which the ras oncogene appears to inhibit the EGF-receptor/kinase and the mechanism by which EGF enhances cytosolic serine kinase activity.